The present invention relates to the dehydration of a gas containing moisture. The process for dehydration of a gas according to the present invention recovers substantially all of the gas in a dry form.
There are a variety of gases from which it is desirable to remove water vapor. The present invention relates particularly to those gases wherein it is highly desirable to recover substantially all of the gas from the dehydration process. The particular gases to which the present invention relates include air, natural gas, nitrogen, methane, carbon dioxide, carbon monoxide and hydrogen, and certain other hydrocarbon gases such as ethane, ethylene, propane, propylene, and the like. Frequently these gases will contain relatively small amounts of moisture in the form of water vapor, but it is still desirable to further dehydrate the gas removing at least about 95% of the moisture present.
The presence of water vapor in these gases can cause problems such as corrosion if the gas also contains carbon dioxide or hydrogen sulfide. It is necessary to reduce the presence of water vapor to a very small amount when transporting the gas or subjecting the gas to subsequent processing e.g., liquefaction or marketing. Reducing moisture in hydrocarbon containing gases is important to eliminate the risk of forming solid deposits of hydrate complexes.
Processes used currently include cooling, contact with glycol, adsorption using silica gels and adsorption using molecular sieves. These processes require very large installations and therefore drive the cost of the process substantially upward. When drying a gas such as natural gas, which is generally piped directly from the gas field to the user, diversion through a batch-type process is expensive and time consuming.
The use of permeable membranes to separate the water vapor from a gas is considered a passive system in that the flow of the gas continues uninterrupted and the system is automated and requires little, if any, tending by personnel. In addition, a membrane system is adaptable to fields, sea platforms and in-plant settings. However, even with the simplicity of membrane systems, it is important to recover substantially all of the gas as gas almost devoid of moisture.
For example, patents relating to dehydration of natural gas by use of membrane systems include U.S. Pat. Nos. 3,735,558 to Skarstrom, et al.; 4,497,640 to Fournie, et al.; and 4,718,921 to Ube Industries. Whereas these patents provide membranes and systems for dehydration of gases, each of the patents sends a significant portion of the gas to waste.
The present invention provides a process for the dehydration of a gas wherein the moisture content is reduced almost entirely while simultaneously recovering substantially all of the gas, the gas being all gas components except water vapor.